By the use of fractionated antigens in ELISA it was possible to correlate length schistosome infection with humoral antibody response. One fraction reacted primarily with antibody in patients with acute or early schistosomiasis while another fraction reacted with sera from patients with chronic infections. An ELISA for the detection of immune complexes has been developed. Limits of sensitivity and 95% confidence limits have been established. Patients with lupus and rheumatoid with positive Clq binding also have positive ELISA Clq. The ELISA Clq is being used to detect immune complexes in sera from patients with filariasis and will be expanded to include schistosomiasis and malaria.